The present invention relates to friction stir welding along a non-linear path, for example, a circular-shaped path.
As disclosed in Japanese application patent laid-open publication No. Hei 9-309164 (EP 0797043 A2), a friction stir welding is a method in which, by rotating a round rod (hereinafter called xe2x80x9ca rotary toolxe2x80x9d), inserting the rotary tool into a welding joint and moving the rotary tool along to the welding line, the welding portion is heated, softened and plastically fluidized and is solid-stately welded.
The rotary tool is comprised of a small diameter portion (called xe2x80x9ca pinxe2x80x9d), which is inserted into the welding joint, and a large diameter portion (called xe2x80x9ca shoulderxe2x80x9d), which is positioned adjacent the small diameter portion of the rotary tool. The small diameter portion and the large diameter portion of the rotary tool have the same axis. The large diameter portion of the rotary tool is driven so that the rotary tool is rotated.
Japanese application patent laid-open publication No. Hei 11-197855, discloses a welding method for use a case in which a welding line between two members has a ring shape (a circular shape). After a start end and a finish end of a welding have overlapped, the finish end is finished in a ring-shaped inner portion or a ring-shaped outer portion of the welding line. Accordingly, after the friction stir welding has been completed and the rotary tool is withdrawn from the welded member, a hole corresponding to the small diameter portion (the pin) of the rotary tool is left in the welded member. When a drawing position is a ring-shaped position to be welded, a problem in the strength of the weld results.
Further, the rotary tool, which comprises a small diameter portion that is inserted into the welding portion and a large diameter portion that is positioned adjacent to and outside of the small diameter portion, is inserted at an angle so s to be inclined relative to the member to be welded. The direction of inclination is such that, in a moving direction (a direction to be welded) of the rotary tool, the small diameter portion of the rotary tool is positioned in front of and leads the large diameter portion of the rotary tool. In other words, the rotary tool is inclined to the rear relative to the direction of movement. The above fact is disclosed also in Japanese patent laid-announcement No. Hei 9-508073 (EP 0752926 B1).
In Japanese application patent laid-open publication No. Hei 11-197855, the inclined rotary tool is moved along a circular path. However, it is extremely difficult to move an inclined rotary tool along a path having a circular shape. To accommodate various kinds of circular shapes, it has been suggested that the welding should be carried out using a numeric control type machine tool. In this type of machine tool, the member to be subjected to welding is fixed to a table, the rotary tool is installed on a main shaft of the machine tool, the main shaft is inclined relative to the table, and the main shaft is moved along a path having a circular shape. However, to maintain a predetermined inclination angle of the main shaft in a circular moving direction, it is necessary to vary the inclination angle with movement along the circular path; and, as a result, the preparation of programs to control such movements is not easily carried out.
An object of the present invention is provide to a friction stir welding method in which welding along a path having a ring shape or a circular shape (a circular arc is included) during the friction stir welding can be carried out easily.
The above-stated object can be attained by a friction stir welding method, characterized in that a first member and a second member are fixed on a table of a machine tool having a main shaft onto which a rotary tool is installed; and then, the table is rotated relative to an axial center of the desired non-linear welding line, and also relative to the direction in which the first member and the second member are to be welded, under a state in which the table is inclined, so as to effect relative movement between the members to be welded and the rotary tool, thereby carrying out friction stir welding of the first and second members.